Post Reply - A new pandemic

Over the past few years China has confirmed at least 3 H3N8 infections in humans, causing severe illness and at least 1 death. While these were due to avian (AIV) H3N8, this influenza subtype can also be found in Canines (CIV), Equines (EIV), and even marine mammals.

There are subtle, genetic differences between the AIV, CIV, and EIV versions of this subtype, and while each pretty much stays in its own lane, spillovers have occurred. 

Originally, Canine H3N8 evolved directly from Equine H3N8, when it abruptly mutated enough to adapt to a canine host, and rapidly began to spread among greyhounds at a Florida race track in 2004 (see EID Journal article Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida).

While equine H3N8 isn't typically thought as a zoonotic disease, it has been shown experimentally capable of infecting both pigs (see J.Virol.: Experimental Infectivity Of H3N8 In Swine) and cats (see Equine influenza A(H3N8) virus infection in cats).

In 2019, an EID Journal Historical Review of Equine H3N8 warned:

Volume 25, Number 6—June 2019
Historical Review
Equine Influenza Virus—A Neglected, Reemergent Disease Threat 

The H3N8 subtype has undergone significant antigenic evolution, resulting in the emergence of distinct lineages, including Eurasian and American, with the Florida sublineage being particularly prevalent. Continuous genetic surveillance and regular updates to vaccine formulations are necessary to address antigenic drift and maintain vaccination efficacy.

Additionally, rare cross-species transmissions have raised concerns regarding the zoonotic potential of EIV. This review provides a comprehensive overview of the epidemiology, pathogenesis, and prevention of EI, emphasizing vaccination strategies and addressing the socio-economic consequences of the disease in regions where the equine industry is vital.

          (Continue . . . ) 

In 2016, in Epizootics, Host Ranges, and Conventional Wisdom we looked at the history of equine epizootics - including the panzootic of 1872 - and at a study (see A Review of Evidence that Equine Influenza Viruses Are Zoonotic) that argued that human EIV infections occasionally occur.

While H3N8 remains pretty far down our zoonotic worry list, novel viruses have a long history of coming at us from out of left field.  And given its continued evolution across multiple lineages (AIV, CIV, EIV), H3N8 is worthy of our attention.